Field of the Invention
The invention lies in the semiconductor technology field. More specifically, the present invention relates to a compensation component having a semiconductor body with a reverse-biasing pn junction, a first zone of a first conductivity type, which is connected to a first electrode and adjoins a zone of a second conductivity type, opposite to the first conductivity type, forming the reverse-biasing pn junction, and having a second zone of the first conductivity type, which is connected to a second electrode, that side of the zone of the second conductivity type which faces the second zone forming a first surface and, in the area between the first surface and a second surface, which lies between the first surface and the second zone, regions of the first and second conductivity type being interleaved with one another.
Such compensation components are, for example, n-channel or p-channel MOS field effect transistors, diodes, thyristors, GTOs or else other components. However, in the following text, the exemplary embodiment will be a field effect transistor (also referred to in brief as xe2x80x9ctransistorxe2x80x9d).
In relation to compensation components, there have been various theoretical investigations scattered over a long time period (see, for example, U.S. Pat. Nos. 4,754,310 and 5,216,275), in which, however, the objective is specific improvements in the turn-on resistance RSDon and not the stability under current loading, such as, in particular, robustness with regard to avalanche and short circuit in the high-current case with a high source-drain voltage.
Compensation components are based on the mutual compensation of the charging of n-doped and p-doped regions in the drift region of the transistor. The regions are in this case arranged spatially in such a way that the line integral over the doping along a line running vertically to the pn junction in each case remains below the material-specific breakdown charge (for silicon: about 2xc2x71012 charge carriers cmxe2x88x922). In this case, the breakdown charge is linked to the breakdown voltage via the second Maxwell equation.
For example, in a vertical transistor, as is common in power electronics, p-columns and n-columns or plates and so on are arranged in pairs. In the case of a lateral structure, p-conductive and n-conductive layers can be stacked alternately one above another laterally between a trench occupied by a p-conductive layer and a trench occupied by an n-conductive layer (see, U.S. Pat. No. 4,754,310).
As a result of the far-reaching compensation of the p-doping and n-doping, in compensation components the doping of the current-carrying area can be increased considerably, that is to say the n-conducting area for n-channel resistors and the p-conducting area for p-channel resistors, which, in spite of the loss in current-carrying area, results in a considerable gain in the turn-on resistance RDSon. The reverse-biasing ability of the transistor in this case depends substantially on the difference between the two dopings since, for reasons relating to the reduction in the turn-on resistance, a doping of the current-carrying area which is higher by at least one order of magnitude is desirable, managing the reverse voltage requires the controlled setting of the degree of compensation in the rangexe2x89xa6+/xe2x88x9210%. In the case of a higher gain in turn-on resistance, the aforementioned range becomes still smaller. The degree of compensation can thereby be defined by (p-dopingxe2x88x92n-doping)/n-doping or by charge difference/charge of a doping region. However, other definitions are also possible in this context.
In order, then, to provide a robust compensation component of the type mentioned at the beginning which, firstly, is distinguished by a high avalanche resistance and high current-carrying ability before or during breakdown and, secondly, can be produced in a straightforward way with easily reproducible characteristics with regard to the technological range of fluctuation of manufacturing processes, the earlier, commonly assigned German patent DE 198 40 032 C1 provides for the regions of the first and of the second conductivity type in such a compensation component to be doped in such a way that, in areas close to the first surface, charge carriers of the second conductivity type predominate and, in regions close to the second surface, charge carriers of the first conductivity type predominate.
In the case of a compensation component, in the reverse-bias case, the voltage is sustained by p-conductive regions and n-conductive regions located close to one another depleting one another, that is to say the charge carriers of the one region, for example the n-conductive region, electrically xe2x80x9ccompensatexe2x80x9d for the charges in the adjacent p-conductive region. As a result, a zone which is depleted of free charge carriers is formed, that is to say a space charge zone. At small voltages, this has the effect, in the individual planes, of a Predominately horizontally oriented electrical field Eh, which runs at right angles to the connecting direction between the two electrodes. As the voltage increases, an increasing part of the volume of the component is depleted horizontally in this way. Once this horizontally oriented electric field Eh has ultimately reached a maximum at a field strength Eh,Bub, then during any further increase in the voltage across the electrodes, the depletion begins of the semiconductor body or substrate and of the zone forming the reverse-biasing pn junction. A vertical field E is therefore then built up.
An electrical breakdown occurs at a critical field strength Ec when the vertical field assumes a value EBv, for which it is true that:       E    c    =                    "LeftBracketingBar"                                            E              ⇀                        Bv                    +                      E                          h              ,              Bub                                      "RightBracketingBar"            ⇒              E        Bv              =                            E          c          2                -                  E                      h            ,            Bub                    2                    
With appropriate dimensions of individual cells in a compensation component, the horizontal field Eh,Bub assumes only relatively low values, even with high doping levels of the regions of the first and second conductivity type, that is to say xe2x80x9chigh column doping levelsxe2x80x9d, which leads to a low turn-on resistance RDSon, so that the field EBv is of the order of magnitude of Ec. According to the relationship which results from this
xe2x80x83UB(EBv;Eh,Bub)=UBV(EBV)+Uh,Bub(Eh,Bub)
it is therefore possible for a compensation component designed in this way to bias high voltages in reverse in spite of a low turn-on resistance RSDon. In this case, UB designates the breakdown voltage, UBv the vertical breakdown voltage and Uh,Bub the horizontal breakdown voltage.
In the case of power components, a large number of individual components or xe2x80x9ccellsxe2x80x9d are connected in parallel. The requirement on a robust power component in breakdown is a high current, caused by impact ionization, without the power component being destroyed. Destruction occurs when the breakdown current in the power component is distributed only poorly, that is to say the current densities are very high at only a few locations in the semiconductor body. This is the case when only individual cells break down, that is to say if an xe2x80x9cavalanche eventxe2x80x9d is not homogeneously distributed over the semiconductor body.
Because of inhomogeneities in the cell field which are caused by their fabrication, are to some extent only marginally pronounced and cannot be avoided, a breakdown is initially always carried by only a few cells, at low breakdown currents, this being caused, for example, by fluctuations in the doping level. These few cells therefore break down earlier than all the other cells, which leads to an inhomogeneous current distribution. The breakdown will be distributed uniformly over the semiconductor body if, for a cell, the reverse-bias voltage rises with the breakdown current, that is to say there is a positive differential characteristic curve. This is because the more current the component is to supply in total in the case of an avalanche, the more cells break down.
In the case of compensation components, the charge carriers generated at breakdown have the effect of xe2x80x9cdynamic dopingxe2x80x9d, which leads to a corresponding electrical field. This field is superimposed on the field which is generated by the dopant atoms and is referred to as a xe2x80x9cstatic field profilexe2x80x9d.
Since, therefore, the breakdown characteristic of a compensation component is defined by means of the static field profile, the robustness of a compensation component, and therefore a compensation component as well, can therefore be influenced via the design of this static field profile.
One example of this is provided by the above noted German patent DE 198 40 032 C1: there, the level of compensation in the voltage-accepting volume is varied, as viewed in the vertical direction.
It is accordingly an object of the invention to provide a compensation component, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which is further improved with regard to an increased robustness of the compensation component.
With the foregoing and other objects in view there is provided, in accordance with the invention, a compensation component, comprising:
a semiconductor body with a reverse-biasing pn junction;
a first electrode and a second electrode on the semiconductor body;
a first zone of a first conductivity type formed in the semiconductor body and connected to the first electrode and a zone of a second conductivity type, opposite the first conductivity type, adjoining the first zone;
a second zone of the first conductivity type connected to the second electrode;
wherein the zone of the second conductivity type has a first face facing towards the second zone;
mutually interleaved regions of the first and second conductivity types formed in a region between the first face and a second face formed between the first face and the second zone; and
wherein the mutually interleaved regions of the first and second conductivity types are doped such that a location, induced by the doping, of a maximum field strength of an electrical field, composed of a first field running between the first face and the second face and a second field oriented perpendicular thereto, is displaced, by varying the second field but with a free profile of the first field, into a plane defined substantially centrally between, and parallel to, the first and second faces.
In other words, in a compensation component of the type mentioned above, the objects are achieved in that the regions of the first and second conductivity type are doped in such a way that the location, induced by this doping, of the maximum field strength of the electrical field, which is composed of a first field running between the two faces and a second field oriented at right angles thereto, is displaced, by varying the second field but with a free profile of the first field, into a plane which runs substantially in the center between the two faces and parallel thereto. As a result, the voltage-sustaining volume formed by the regions of the first and second conductivity type is preferably divided by the plane into two parts which are each capable of accepting about half the breakdown voltage.
In accordance with an added feature of the invention, a voltage-accepting volume formed by the mutually interleaved regions of the first and second conductivity type is divided by the plane into two parts each capable of accepting approximately half a breakdown voltage.
The first field is preferably a vertical field, and the second field is preferably a horizontal field, so that the compensation component has a vertical structure. However, it may also be a lateral component, if the first field is a horizontal field and the second field is formed by a lateral field. In the following text, a vertical structure is to be assumed first.
In order to be able to achieve the maximum robustness of the compensation component, in the case of a vertical structure, therefore, a breakdown location PAV is displaced into a horizontal plane LH which is characterized by the fact that it breaks down the voltage-accepting volume into two parts, it being possible for about half the breakdown voltage to be accepted by each individual part.
In this case, the horizontal plane LH is preferably located at about half the height of the regions of the first and second conductivity type, that is to say of the charge columns. The further the breakdown location PAv is removed from the horizontal plane LH in the vertical direction, the lower the robustness of the component becomes. The breakdown location PAv is determined by the maximum of the electrical field strength which, for its part, is divided into a horizontal component and a vertical component.
The present invention now utilizes this subdivision of the electrical field into the horizontal field and the vertical field in an advantageous way.
In order to displace the breakdown location PAv into the horizontal plane LH as far as possible in the center between the first and second surfaces, there are in principle two possible ways:
(a) The horizontal field over the regions of the first and the second conductivity type, that is to say as viewed over the column depth z, is not varied, so that the breakdown location is defined via the vertical field. Here, the vertical field exhibits a global maximum in the vertical profile.
(b) The vertical field is not varied, as viewed over the column depth z, so that the breakdown location PAv is defined via the horizontal field. Here, the horizontal field exhibits a global maximum in the vertical profile.
By using the above possible ways (a) and (b) to configure the horizontal field and the vertical field, virtually any desired doping profiles can be specified, said profiles differing from the doping profile described in DE 198 40 032 C1, but being able to achieve the same objective, such as in particular high robustness for a compensation component.
Corresponding considerations also apply to a lateral component.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a compensation component with improved robustness, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of the specific embodiment when read in connection with the accompanying drawings.